Process for alkenylation of alkylbenzenes

ABSTRACT

An improvement is disclosed in the alkenylation of alkylbenzenes with conjugated alkadienes in excess alkylbenzene to increase the yield of the mono-adduct product. The improvement involves an economical manner of substantially increasing the amount of alkylbenzene recycle without increasing the size of the distillation column normally used to separate the alkylbenzene from the mono-adduct in the reaction product. Since mono-adduct yield is directly proportional to the amount of excess alkylbenzene a significant yield increase is obtained without a significant increase in distillation column cost.

United States Patent 1 1 Mitchell 1 1 Feb. 11, 1975 PROCESS FORALKENYLATION OF Primary E.raminer-C. Davis ALKYLBENZENES Attorney,Agent, or Firm-George L. Church; Donald 75 Inventor: Richard E.Mitchell, Boothwyn, Pa. Edward Hess [73] Assignees: Sun Ventures lnc..St. Davids. Pa.: [57] ABSTRACT Lmmed Tokyo Japan An improvement isdisclosed in the alkenylation of al- [22] Filed: Oct. 31, 1973kylbenzenes with conjugated alkadienes in excess alkylbenzene toincrease the yield of the mono-adduct [211 Appl' product. Theimprovement involves an economical manner of substantially increasingthe amount of al- [52] U5. Cl. 260/668 B, 260/671 A kyl nzene recycl ihout increasing the size of the [51] Int. Cl. C07c 3/52 di illationcolumn normally used to separate the al- [58] Field of Search 260/668 8.671 A kyl enzene from the mono-adduct in the reaction product. Sincemono-adduct yield is directly propor- [56] References Cit d tional tothe amount of excess alkylbenzene a signifi- UNITED STATES PATENTS cantyield increase is obtained without a significant in- 3,766,288 10/1973Shima et al, 260/668 B crease m d'smlaton Column cost 8 Claims, 1Drawing Figure O-XYLENE l5 FEED I4 it MOLTEN ALKALI METAL I3 I I6 H 2627 28 29 30 M M M M M 2| A B C D E VA. i /i i i t2 I8 22 23 24 .25 37 46,32 33 54 35 K36 I9 3 o X 1 6E BUTADlENE 4 2o FEED 38 FLASH CHAMBERSETTLER :3 PRODUCT E Q HEAVY ENDS DISTILLATION PATENTED'FEBI 1 I9153.865889 O-XYLENE l5 FEED I l I4 /|'0 {I MOLTEN ALKALI 7 Y METAL I3 I I6H i /E cjlozjczfilcjco 2 37 IAVAA 4 BUTADIENE FEED FLASH CHAMBER PRODUCTHEAVY ENDS PROCESS FOR ALKENYLATION OF ALKYLBENZENES BACKGROUND OF THEINVENTION The alkenylation of alkylbenzenes can be used as a route forpreparing various alkylnaphthalenes by following the alkenylationreaction with a ring closure step to form an alkyltetralin and then adehydrogenation step to produce the corresponding alkylnaphthalene. Forexample, the reaction of butadiene with toluene gives l-phenylpentenewhich upon ring closure forms l-methyltetralin which can bedehydrogenated to l-methylnaphthalene. Other examples of analogousconversions are 1,5-dimethylnaphthalene from oxylene and1,7-dimethylnaphthalene from p-xylene. These dimethylnaphthalenes can beisomerized, respectively, to the 2,6- and 2,7-isomers, as described byG. Suld et al., J. ORG. CHEM., 29, 2936-2946 (1964); and the 2,6- and2,7-isomers can be oxidized to the corresponding diacids useful formaking polyester resins, as disclosed in U.S. Pat. No. 3,293,223, issuedDec. 20, 1966, lrl N. Duling.

This invention relates to the catalyzed reactions of alkylbenzenes withconjugated alkadienes to produce the mono-adduct product, i.e. theone-to-one addition product of the alkylbenzene and diene.

The use of alkali metals for promoting the addition of alkadienes toalkylbenzenes is known in the prior art. This kind of reaction is shownfor such reactants as toluene or xylene with butadiene or isoprene inthe following U.S. Pat. Nos: 1,934,123 issued Nov. 7, 1933, F. Hofmannct al.; and 2,603,655, issued July 15,1962, D. E. Strain. Suchalkenylation reactions have also been described by R. E. Robertson etal., CAN. .1. RES, 263, 657-667 (1948). However the conditions disclosedin these references result in the production of large amounts of adductsof higher molecular weight than the mono-adduct product. Thesereferences fail to provide conditions under which the mono-adductproduct could be obtained in high yield.

Conditions more favorable for securing good yields of the mono-adductproduct in such alkenylation reactions have been described by G. G.Eberhardt et al. in J. ORG. CHEM., 30, 82-84 (1965) and in EberhardtU.S. Pat. No. 3,244,758, issued Apr. 5, 1966. The conditions describedin these references include utilizing a granular support on which thealkali metal is distended and slowly adding the conjugated diene to thealkyl aromatic reactant while vigorously agitating the mixture. Whilethese conditions result in good yields of the mono-adduct, neverthelesssubstantial amounts of higher adducts are formed. For example, in thereaction of o-xylene with butadiene in the disclosed manner, thealkenylated product typically contains 80-85 percent by weight ofmono-adduct (i.e. odolylpentene) with the remainder being mainlydi-adducts.

The principal by-product formed is the di-adduct addition product formedby the combination of two alkadiene molecules with one alkylbenzenemolecule, although even higher adducts are formed in small amounts.

One method of reducing by-product formation is to reduce theconcentration of mono-adduct in the reaction zone. Since the amount ofhigher adducts formed is proportional to the concentration ofmono-adduct in the reaction zone, procedures for reducing the monoadductconcentration will reduce by-product formation and improve mono-adductyield.

My copending application, Ser. No. 398,112, filed Sept. 18, 1973, andincorporated herein by reference, discloses a method for reducing themono-adduct concentration which involves passing the alkylbenzenethrough a series of successive reaction zones substantially isolatedfrom each other while adding alkadiene to each zone, the totaldiene:alkylbenzene mole ratio being less than 0.511.

In this system the average concentration of monoadducts in the slurryfor the serially arranged reaction zones is less than the mono-adductconcentration would be for a single stage reaction system. In the latterthe final mono-adduct concentration is also the concentration alwaysmaintained in the reactor; whereas in a plurality of successive zonesthe final mono-adduct concentration is only that in the last zone andthe average concentration thereof for all zones is considerably less.Since the amount of higher adducts formed is proportional to theconcentration of mono-adducts in the reaction zone the use of aplurality of stages in the manner described substantially improvesselectivity for the desired product.

My aforesaid copending application also discloses carrying out thealkenylation reaction in the presence of excess alkylbenzene. This alsohas the effect of reducing the mono-adduct concentration in the reactionzone and thereby, for the reasons mentioned previously, increasingmono-adduct yield.

When excess alkylbenzene is employed the reactor cffluent is sent to adistillation column (after removal of any catalyst particles) and theexcess alkylbenzene is separated from the adduct products. The latterare sent to another distillation column where pure monoadduct isdistilled. The separated excess alkylbenzene is recycled to the reactionzone.

Although alkylbenzenezalkadiene weight ratios of greater than, say, 20:1are desired to maximize monoadduct yield a distinct disadvantage arisesat such a high ratio. This is because all the excess alkylbenzene mustbe distilled in the above-mentioned distillation column. A point isreached where the increase in column size resulting from an increase inthe alkylbenzenezalkadiene ratio is not justified even though thisincreased ratio begets a significant increase in monoadduct yield.

SUMMARY OF THE INVENTION The invention provides a means for increasingthe alkylbenzenezalkadiene ratio that can be employed in thealkenylation reaction without excessive costs. Stated in another mannerthe invention provides a means of increasing the maximum economicalalkylbenzene recycle ratio in the alkenylation of alkylbenzenes with analkadiene. The method involves reacting the alkadiene with excessalkylbenzene, which excess includes recycle alkylbenzene, and, at theend of the reaction, introducing the reaction mass into a flash chamber,flashing off some of the alkylbenzene for use as some of the recycle,introducing the remaining reaction mass into a distillation column toseparate adduct product plus more alkylbenzene and utilizing the latteralso as recycle.

The flash chamber is considerably cheaper than additional multiplatedistillation capacity and functions just as well. As a result thedistillation column for the same 3 recycle ratio is smaller or, betteryet, additional recycle can be achieved with the same distillationcolumn.

BRIEF DESCRIPTION OF THE DRAWING One embodiment of the invention isillustrated in the accompanying drawing which is a diagrammaticflowsheet of the process.

DESCRIPTION OF THE INVENTION The alkylbenzene reactant for the presentprocess can have one to four alkyl groups, and it should contain atleast three benzylic non-tertiary hydrogen atoms per molecule. The termbenzylic hydrogen" refers to a hydrogen atom attached to a carbon atomwhich is directly attached to the benzene ring. Thus toluene ordiethylbenzene meets the requirement of containing at least threebenzylic nontertiary hydrogen atoms, but ethylbenzene does not.Triisopropylbenzene, while having three benzylic hydrogen atoms, alsodoes not since they are tertiary hydrogen atoms. The size andconfiguration of the alkyl substituents on the benzene ring areimmaterial as long as three or more benzylic hydrogen atoms which arenon-tertiary are present. Generally the number of carbon atoms in eachalkyl group will be in the range of l-10 and usually 1-2.

The following are illustrative examples of suitable alkylaromatics whichcan be alkenylated in an improved manner by means of the presentprocess: toluene; mor p-xylene; mesitylene; pseudocumene; hemimellitene;durene; isodurene; prehnitene; methylethylbenzenes; cymenes;di-n-propylbenzenes', tri-nhexylbenzenes; ethyldecylbenzenes;methyl-tbutylbenzenes; and the like.

The diene reaction is a C -C conjugated alkadiene, viz. 1,3-butadiene,1,3-pentadiene and isoprene.

Both reactants should be substantially free of water, sulfur compoundsor other impurities, as otherwise excessive loss of deactivation ofcatalyst may occur. Water can conveniently be removed from the feedmaterials by treatment with a molecular sieve adsorbent.

Alkenylation of the alkylbenzene by reaction with the diene ispreferably promoted by means of potassium, sodium or a potassium-sodiummixture but other catalysts known in the art may be employed. Preferablythe alkali metal promoter is composed of a major proportion of sodiumand a minor proportion of potassium on a weight basis, such as 75-98parts sodium to 2-25 parts potassium. Normally only a small proportionof alkali metal to the alkylbenzene reactant is employed, such as0.015.0 g. moles alkali metal per liter of alkylbenzene and preferably0.1 to 1.0 g. and a minor proportion of potassium on a weight basis,such as 75-98 parts sodium to 2-25 parts potassium. Normally only asmall proportion of alkali metal to the alkylbenzene reactant isemployed, such as 0.0l5.0 g. moles alkali metal per liter ofalkylbenzene and preferably 0.1 to 1.0 g. mole per liter. The catalystis not considered to be the alkali metal per se but rather themetallo-organic product resulting from reaction of at least part of thealkali metal with the alkylbenzene. For instance, in the alkenylation oftoluene employing potassium as promoter, the effective catalyst isbelieved to he the reaction product, benzyl potassium, which forms whena dispersion or slurry of molten potassium in heated toluene stands.Thus in order to obtain the catalyst, the alkali metal needs to be incontact with the alkylbenzene at a temperature above the melting pointof the metal for enough time to permit substantial reaction. Therespective melting points of K and Na are 623C and 975C but alloys ofthese metals exhibit lower melting points. For example. a 50:50 byweight mixture of the two has a melting point of 10C. However. since thereaction between the metal and alkylbenzene is slow at low temperatures,it is advantageous to maintain the temperature of the dispersion atleast above 50C to form the metallo-organic catalyst. The latter isslightly soluble in the aromatic hydrocarbon but mainly will be presentas a dispersed solid.

The accompanying drawing illustrates the improved method of alkenylatingalkylbenzenes in accordance with the invention. For purpose ofdescribing the process, the reactants are considered to be o-xylene andbutadiene and the promoter. The desired reaction for producing themonoadduct product is illustrated by the following equation (hydrogenatoms being omitted for simplicity):

o-xylene butadiene 5-o-tolylpentene-2 As shown, the desired product fromthese reactants is 5-o-tolypentene-2, which can be converted to1,5-dimethyltetralin by treatment with an acid catalyst. During thisreaction substantial amounts of higher adducts tend to form due to thereaction of more than one mole of butadiene per mole of o-xylenereacted. Reaction of the additional butadiene can occur in several waysto produce higher adducts of various structures. The present methodminimizes the formation of these higher adducts by carrying out thealkenylation reaction in the presence ofa large excess of o-xylene whichis obtained by a much more economical procedure than heretoforeemployed. This excess results in substantially higher selectivity inconversion of the oxylene to the desired mono-adduct than otherwise canbe secured.

Referring now to the drawing, o-xylene feed in line 10 is mixed withrecycled o-xylene from line 11 and then continues through line 10 toheater 12 wherein it is heated to the desired temperature. A minorproportion of the o-xylene is diverted through line 13 to a catalystpreparation tank 14 containing heater 15. Molten alkali metal obtainedfrom a source not shown is drawn through line 16 into catalystpreparation tank 14. The latter is provided with a motorized stirrer notshown for effectively dispersing the alkali metal in the hydrocarbon.The temperature in tank 14 is usually held in the range of 50-l70C, morepreferably 140C, to facilitate reaction of the alkali metal and o-xyleneand form the metallo-organic catalyst.

The alkali metal, can be potassium or sodium or any mixture or alloy ofthese two metals. The effective catalyst tends to form more readily whenpotassium is used than when sodium alone is employed and the selectivityfor mono-adduct production appears to be somewhat better. Howevermixtures of sodium and potassium containing even as much as percent ormore sodium are about as effective as potassium alone. In view of thefact that sodium usually is less expensive than potassium it isdistinctly preferred that the alkali metal utilized be composed of amajor proportion of sodium and a minor proportion of potassium on aweight basis.

Within the zone where the alkenylation reaction occurs, it is desirableto maintain the Na:l( proportion within the range of 75:25 to 98:2 and aproportion of about 95:5 is preferred. At this weight proportion theloss of alkali metals from the system due to solubility of theirderivatives in the hydrocarbon phase generally involves roughly twice asmuch sodium as potassium. Accordingly, about a two-to-one NazK rationeeds to be maintained for the alkali metals added as makeup throughline 16 in order to maintain the 95:5 preferred proportion in thesystem.

The proportion of alkali metal to alkylbenzene in catalyst preparationtank 14 is not critical and can vary widely. Generally from 5 to 20parts by weight of the alkylbenzene per part of alkali metal are used inpreforming the catalyst dispersion. The minimum residence time in tank14 for forming the catalyst will vary with temperature, decreasing ashigher temperatures are employed. Typically, for a temperature level of1 C, a residence time of 0.5-2.0 hours is employed.

The catalyst dispersion flows from tank 14 through line 17 to line 18where it meets the stream of o-xylene from heater 12. Also meeting thestream of o-xylene from heater 12 in line 18 is o-xylene recycle in line19 from flash chamber 20. As will be explained hereafter this recycle isnormally at about the boiling point of oxylene (144C) and will usuallybe vapor. In any event the heat input in heater 12 should be such thatthe oxylene feed in line 10 plus the recycle in line 11, both of whichare usually well below the o-xylene boiling point, plus the line 19recycle and line 17 catalyst addition, yield a total mixture at about144C at the inlet to reactor 21.

The amount of o-xylene recycled should be such that the total o-xylene(i.e., recycle plus makeup) is at least pounds per pound of totalbutadiene (i.e., line 31 butadiene). Normally this ratio will be atleast 20:1, preferably at least :1. The data below show the improvedmono-adduct yield (moles momo-adduct per mole of butadiene times 100) atdifferent o-xylene ratios (pounds total o-xylene divided by poundsbutadiene) at typical operating conditions. By employing my inventionyields of at least 84 percent are obtained, usually at least 86-88percent.

o-Xylene Mono-a dduct Ratio Yield Reactor 21 is preferably divided intoseveral independently stirred reaction zones. The number of such zonescan vary, for example, from 2-10 but preferably is in the range of 3-6.As illustrated in the drawing, five independent zones, designated by A,B, C, D and E, are utilized. The zones are separated by baffles 22, 23,24 and 25 each of which is somewhat spaced from the top of tank 21 topermit overflow of the reaction mixture to the next zone. The zones areprovided with motorized stirrers 26, 27, 28, 29 and 30 and withindividual spargers not shown at the bottom of each zone forindependently admitting a continuous stream of butadiene from feed line31 to each reaction zone via lines 32, 33, 34, 35 and 36.

Effective mixing conditions are maintained in each of zones A, B, C, Dand E by the respective motorized mixers, and the butadiene is fedrelatively slowly through the sparger provided in each zone. Thebutadiene in each zone is thus immediately dispersed into the slurry ata rate whereby a low concentration of the diene therein is maintained.Preferably each zone has about the same volumetric capacity and therates of butadiene addition to the zones are approximately the same,although this is not essential. The amount of total diene to all fivezones is preferably controlled so as to provide less than 0.5 mole dieneper mole of o-xylene feed. Best results are usually obtained by holdingthis ratio in the range of 0.5-0.30 mole diene per mole of o-xylene fedthrough line 18 to reactor 21. The slurry of catalyst in o-xylene passesfrom the inlet end of reactor 21 successively through the series ofreaction zones, flowing over the baffles 22, 23, 24 and 25 from one zoneto the next. The final slurry from reaction zone E passes out of reactor21 via line 37.

The reaction in reactor 21 is exothermic and, if necessary, reactor 21can be provided with cooling coils or other heat removal means (notshown) to keep the temperature constant from inlet to outlet. Theprocess can also be conducted, however, by introducing the slurrythrough line 18at somewhat below the average desired temperature andallowing the temperature to rise above the average level as the mixtureflows to outlet line 37.

The above-described staged reactor system is the preferred manner ofcarrying out the present invention and is described and claimed in myaforesaid copending application. By using several independently stirredreaction zones with separate butadiene feed streams, as compared with asingle reaction zone to which both reactants are fed continuously,permits a substantial increase in selectivity for mono-adductproduction, i.e., this arrangement materially reduces the percentage ofthe reacted o-xylene that is converted to di-adducts and other higheradducts. On the other hand the staged reactor system is not essential tothe success of the present invention and insofar as the latter isconcerned it can be employed with either a one-stage or a multistagereactor. My aforesaid copending application shows the improvedmono-adduct selectivity that can be achieved by staging. The datahereinabove show the improvement achieved by higher recycle ratios.

The reaction mixture next passes to settler 38 wherein the alkali metal,including that in the form of undissolved metallo-organic catalyst, isallowed to settle from the bulk of the hydrocarbon phase. The alkalimetal solid material is removed from the settler 38 by line 39 anddiscarded. If desired the catalyst can be recycled by means not shown tocatalyst preparation tank 14 for reuse but in most cases very smallamounts of catalyst are employed and it will be more economical todiscard the catalyst rather than recycle it. In some cases, depending onreactor 21 temperature, a cooler, not shown, will be employed in line 37between reactor 21 exit and settler 38 but the reaction mixture ispreferably not cooled much below the o-xylene boiling point.

From the upper part of settler 38 the hydrocarbon phase is withdrawn vialine 40 and is sent to flash chamber 20, which is equipped with heatingmeans 41. Flash chamber 20, is in effect a single stage vaporizer asopposed to a distillation column which has many stages to achievedesired purities. However in one stage o-xylene recycle containing 90+%o-xylene can be obtained by heating the catalyst-free reaction productmixture to its boiling point by heating means 41. The vapor exits theflash chamber through line 19 to meet o-xylene feed in line 18.

The material entering the flash chamber will normally be at about theboiling point of o-xylene. Accordingly any heat supplied via means 41will result in some o-xylene vaporization. On the other hand heat doesnot need to be the means by which o-xylene is separated in flash chamber20. For example the chamber could be maintained under vacuum so that assoon as reaction product entered it would vaporize in part.

1t will now be apparent that the heat input in heater 12 will depend,inter alia, upon the temperature of the o-xylene in line 19. In somecases a condenser may be employed in line 19 to condense the flashchamber vapors, depending on how flash chamber 20 is operated. This willalso affect heater 12 input.

Normally the amount of o-xylene separated in flash chamber 20 will be atleast 20 percent by weight of the total recycled o-xylene, i.e., line 11plus line 19 oxylene. Preferably the amount is at least 30 percent, morepreferably at least 40 percent.

From the bottom of flash chamber 20 the unvaporized material iswithdrawn through line 42 and sent to fractional distillation tower 43.The unreacted o-xylene is removed overhead via line 44, cooled incondenser 45 and passes to recycle tank 46. The recovered oxylene isrecycled for reuse through line 11. The relatively pure mono-adductbottoms from tower 43 pass through line 47 to a second distillationcolumn 48 from which the desired mono-adduct product is recovered viaoverhead line 49. The higher adduct material, obtained in minorproportion as bottoms through line 50, is composed principally ofdi-adduct with lesser amounts of tri-adduct and higher material.

The following are specific examples of the process of the inventioncompared with a process which does not utilize my improvement.

In a conventional manner, not employing a flash chamber, 167 parts ofo-xylene per unit time are fed to the system (line 10). Fresh o-xyleneat this rate admixes with 1,500 parts of recycled o-xylene from line 11and most of the mixture passes through heater 12, where the temperatureis raised to 145C, and then to reactor tank 21. About 6 parts of the 167parts of oxylene are diverted through line 13 and heated to l1l5C intank 14 and are mixed in tank 14 with 0.7 parts sodium and 0.3 partspotassium. After an average residence time of about one hour in tank 14,the resulting catalyst dispersion flows through line 17 to reactor 21.100 parts butadiene (line 31) is added to the reactor. The latterpreferably is provided with cooling means to prevent the temperaturefrom rising above; l45-150C as the reaction occurs and also preferablyis of a size such that the total residence time in the tank is 2-3hours. The slurry leaving reactor 21 through line 37 (1,770 partsexcluding catalyst) passes through settler 38 whereby the alkali metalcomponents are separated from the bulk of the hydrocarbon phase. Thehydrocarbon phase (1,767 parts) is sent directly to distillation column43 (bypassing flash chamber in which 1,500 parts of o-xylene arerecovered for recycling. The bottoms from column 43 are distilled incolumn 48 to yield an overhead product containing 245 parts mono-adduct.

The above example is repeated except that flash chamber 20 is employed.The fresh o-xylene feed is the same, 167 parts. The line 11 recycle is1,500 parts and line 19 recycle is 833 parts making a total feed toreactor 21 of 2,500 parts. pounds of butadiene are added and 2600 partsreaction product (excluding catalyst) are removed through line 37 andultimately enter flash chamber 20 at a temperature of about 144C. Heatis supplied via heater 41 to vaporize 833 parts 0- xylene enters line 18via line 19. The balance of 1,767 parts is distilled in distillationcolumns 43 and 48 as in the first example with 271 parts of mono-adductbeing recovered overhead in line 49.

It is apparent from the above that increased o-xylene recycle has beenachieved by means of the flash chamber. The total o-xylene to butadieneratio being 16.721 and 25:1 in the first and second examplesrespectively. In both examples, however, the amount of materialdelivered to distillation column 42 is the same. The yield improvementfrom the higher recycle ratio is evident.

Analogous results can be obtained in the alkenylation of otheralkylbenzenes by conjugated diolefins by the procedure of the invention.Other particularly useful alkenylations are the reaction of toluene withbutadiene to given phenylpentene and the reaction of other xylenes withbutadiene to yield other tolylpentenes, via m-tolylpentene-Z fromm-xylene or p-tolylpentene-Z from p-xylene.

The invention claimed is:

1. In a process in which an alkadiene is reacted with excessalkylbenzene including recycle alkylbenzene hereinafter specified toform a reaction mass containing the mono-adduct alkadiene-alkylbenzeneaddition product, the reaction mass is fractionated in a distillationcolumn to separate a relatively pure mono-adduct and alkylbenzene, thelatter being employed as said recycle, the improvement which comprises:

a. introducing the reaction mass to a flash chamber to separate aportion of the alkylbenzene therein;

b. fractionating the remaining reaction mass in said distillation columnto separate relatively pure monoadduct and additional alkylbenzene;

c. and employing alkylbenzene separated in both the flash chamber andthe distillation column as said recycle.

2. Method according to claim 1 wherein said alkylbenzene is o-xylene andsaid alkadiene is butadiene.

3. Method according to claim 2 wherein the ratio of total o-xylene tobutadiene is at least 25 to l by weight.

4. Method according to claim 2 wherein at least 20 weight percent of therecycled o-xylene is separated in the flash chamber.

d. introducing remaining material into a distillation zone; e.separating additional o-xylene in the distillation zone to producerelatively pure 5-o-tolylpentene-2; f. utilizing o-xylene separated in(c) and (e) as said recycle. I 7. Method according to claim 6 whereinthe ratio of total o-xylene to butadiene is at least 25 to l by weight.8. Method according to claim 6 wherein at least 20 percent of therecycled o-xylene is separated in the flash chamber.

1. IN A PROCESS IN WHICH AN ALKADIENE IS REACTED WITH EXCESSALKYLBENZENE INCLUDING RECYCLE ALKYLBENZENE HEREINAFTER SPECIFIED TOFORM A REACTION MASS CONTAINING THE MONO-ADDUCT ALKADIENE-ALKYLBENZENEPRODUCT, THE REACTION MASS IS FRACTIONAL IN A DISTILLATION COLUMN TOSEPARATE A RELATIVELY PURE MONO-ADDUCT AND ALKYLBENZENE, THE LATTERBEING EMPLOYED AS SAID RECYCLE, THE IMPROVEMENT WHICH COMPRISES: A.INTRODUCING THE REACTION MASS TO A FLASH CHAMBER TO SEPARATE A PORTIONOF THE ALKYLBENZENE THEREIN; B. FRACTIONATING THE REMAINING REACTIONMASS IN SAID DISTILLATION COLUMN TO SEPARATE RELATIVELY PURE MONOADDUCTAND ADDITIONAL ALKYLBENZENE; C. AND EMPLOYING ALKYLBENZENE SEPARATED INBOTH THE FLASH CHAMBER AND THE DISTILLATION COLUMN AS SAID RECYCLE. 2.Method according to claim 1 wherein said alkylbenzene is o-xylene andsaid alkadiene is butadiene.
 3. Method according to claim 2 wherein theratio of total o-xylene to butadiene is at least 25 to 1 by weight. 4.Method according to claim 2 wherein at least 20 weight percent of therecycled o-xylene is separated in the flash chamber.
 5. Method accordingto claim 2 wherein the yield of mono-adduct product is over 84 percentby weight based on butadiene.
 6. Method which comprises: a. reactingbutadiene with excess o-xylene, including recycle o-xylene from step(f), in a reaction zone to form reaction product containing5-o-tolylpentene-2; b. removing reaction product from the reaction zoneand introducing same into a flash chamber; c. separating in the flashchamber a portion of the o-xylene in the reaction product; d.introducing remaining material into a distillation zone; e. separatingadditional o-xylene in the distillation zone to produce relatively pure5-o-tolylpentene-2; f. utilizing o-xylene separated in (c) and (e) assaid recycle.
 7. Method according to claim 6 wherein the ratio of totalo-xylene to butadiene is at least 25 to 1 by weight.
 8. Method accordingto claim 6 wherein at least 20 percent of the recycled o-xylene isseparated in the flash chamber.